1. Field
The present disclosure relates to a process for the continuous preparation of a catalytic system that can be used for the polymerization of at least one conjugated diene monomer, and to an installation for implementing said process.
2. Description of Related Art
Patent documents WO-A-02/38636 and WO-A-03/097708 in the name of the applicants teach, in order to polymerize conjugated dienes, to use a “preformed” type catalytic system based on at least:                a preforming conjugated diene, such as butadiene;        an organic phosphoric acid salt of one or more rare-earth metals, which is in suspension in at least one saturated and aliphatic or alicyclic, and inert hydrocarbon-based solvent, this or these rare-earth metal(s) being present in said catalytic system in a concentration, for example, approximately equal to 0.02 mol/l and preferably ranging from 0.01 to 0.06 mol/l;        an alkylating agent composed of an alkylaluminium having the formula AlR3 or HAlR2, in which R represents and alkyl radical, preferably of 1 to 8 carbon atoms, and H represents a hydrogen atom; and        a halogen donor composed of an alkylaluminium halide.        
The catalytic systems described in these documents are prepared in batch mode by implementing, in the same reactor, the following steps:                in a first optional step of solvation, a suspension of said salt of rare-earth element(s) is prepared in said inert hydrocarbon-based solvent;        in a second step, the conjugated diene is added to the suspension obtained in the first step or else, in the case where the first step has not been carried out, said solvent in addition to said conjugated diene is added to said salt;        in a third step of alkylation, said alkylating agent is added to the suspension obtained at the end of said second step in order to obtain an alkylated salt;        in a fourth step of halogenation, said halogen donor is added to said alkylated salt, producing a highly exothermic reaction of formation of a prepolymer of said conjugated diene; then        in a fifth step of ageing, the mixture thus obtained is maintained at a constant temperature of approximately 60° C. for one to two hours, in order to obtain the preformed catalytic system, which is typically stored at a temperature of −15° C.        
A major drawback of this process for preparing the preformed catalytic system in batch mode is that, in addition to the cycle time of several hours that it requires, if it is designed to increase the final concentration or rare-earth element(s) in the catalytic system, it is necessary to increase, in accordance with the latter, the concentration of preforming conjugated diene, thereby generating an increased exothermicity of the preformation step, this increased exothermicity being difficult to control and possibly detrimental to the activity of the catalytic system, or even to the safety of the installation.
This need to provide a relatively long cycle time for the synthesis of this catalytic system and a reduced concentration of rare-earth element(s) in said system, in order to minimize the abovementioned exothermicity, leads to this synthesis being carried out in a reactor having a relatively large volume.
Another drawback of this process for synthesis in batch mode lies in the difficulty in achieving good reproducibility of the catalytic systems obtained under given conditions, and also optimal coupling of this batch process with a polymerization carried out in continuous mode, for example in order to obtain polybutdiene or polyisoprene.
Patent document US-A-2004/0116638 mentions the possibility of preparing such catalytic systems, in continuous mode, by bringing into contact, in a feed line for feeding a polymerization reactor with conjugated diene, at a temperature ranging from −20 to 80° C., the preforming conjugated diene in solution with the alkylating agent, then the alkylation product thus obtained with the salt of rare-earth element(s), then finally the halogen donor, the preformed catalytic system resulting therefrom being introduced into the reactor in continuous mode within a period of less than 10 minutes starting from the addition of the halogen donor.
It will be noted that the latter document does not describe, in its single example, the implementation of such a continuous-mode synthesis of the catalytic system, but describes a synthesis of polydienes, the essential characteristic of which consists in maintaining, in the continuous-mode reactor, a non-ideal flow stream of the constituents so as to ensure that 10% of the constituents entering the reactor at a given reference time are present in the continuous-mode reactor at a time t1 which is different from the initial residence time.